The anticoagulation therapy has been extensively performed for the prevention and treatment of thromboembolic diseases caused by accelerating blood clotting, and drugs such as heparin and warfarin potassium have been frequently used as anticoagulant agents at present.
However, it has been known that heparin has an antithrombin activity and activated blood coagulation factor X inhibitory activity and it is apt to cause bleeding tendency.
Warfarin potassium is an anticoagulant which controls biosynthesis of vitamin K-dependent coagulation factor, and it is difficult to control the anticoagulation capacity due to its action mechanism when this drug is used in the prevention and treatment of thromboembolic diseases. Therefore, this drug is extremely difficult to use clinically.
In recent years, selective thrombin inhibitors have been developed and have been used clinically. However, since thrombin plays a close part in the conversion of fibrinogen into fibrin in blood coagulation cascade reactions and platelet activation and aggregation, the thrombin inhibitors also have similar problems to those of heparin from the safety point of view such as bleeding tendency and it has been reported that their effects are not necessarily enough.
On the other hand, activated blood coagulation factor X, which acts at the joining point of the extrinsic and intrinsic blood coagulation cascade reactions, locates upstream to thrombin, so that coagulation inhibition is more efficient than that of thrombin inhibitors and therefore activated blood coagulation factor X inhibitors attract public attentions as drugs having a possibility that such an inhibition acts to the coagulation system effectively.
Furthermore, with the changes into European and American life styles and the increase in aged population in recent years, incidence of thromboembolic diseases such as myocardial infarction and arteriovenous obstruction will go on increasing, and therefore, demands on development of more effective anticoagulants are great and social importance of their treatment has been increasing more and more.